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drm/i915: Add I915_GEM_PARAM_HAS_SEMAPHORES
Userspace tries to estimate the cost of ring switching based on whether the GPU and GEM supports semaphores. (If we have multiple rings and no semaphores, userspace assumes that the cost of switching rings between batches is exorbitant and will endeavour to keep the next batch on the active ring - as a coarse approximation to tracking both destination and source surfaces.) Currently userspace has to guess whether semaphores exist based on the chipset generation and the module parameter, i915.semaphores. This is a crude and inaccurate guess as the defaults internally depend upon other chipset features being enabled or disabled, nor does it extend well into the future. By exporting a HAS_SEMAPHORES parameter, we can easily query the driver and obtain an accurate answer. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
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2 changed files with 4 additions and 0 deletions
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@ -1009,6 +1009,9 @@ static int i915_getparam(struct drm_device *dev, void *data,
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case I915_PARAM_HAS_WAIT_TIMEOUT:
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value = 1;
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break;
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case I915_PARAM_HAS_SEMAPHORES:
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value = i915_semaphore_is_enabled(dev);
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break;
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default:
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DRM_DEBUG_DRIVER("Unknown parameter %d\n",
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param->param);
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@ -311,6 +311,7 @@ typedef struct drm_i915_irq_wait {
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#define I915_PARAM_HAS_LLC 17
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#define I915_PARAM_HAS_ALIASING_PPGTT 18
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#define I915_PARAM_HAS_WAIT_TIMEOUT 19
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#define I915_PARAM_HAS_SEMAPHORES 20
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typedef struct drm_i915_getparam {
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int param;
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